Catalyst For Tar Cracking Research Articles

Catalytic performance of activated lignite chars on biomass tar cracking

The tar problems are the major obstacle to developing the biomass pyrolysis technology. The coal chars derived from in situ pyrolysis and/or partially gasification are a promising alternative tar cracking catalyst with great industrial application potential because of its cheap and easily available characteristics. This work investigated the application of lignite chars as catalysts for biomass tar decomposition. Raw lignite char was further gasified with CO2 for 5min (GC5) and 15min (GC15) and used as tar cracking catalysts. Effects of pyrolysis temperature, char/biomass mass ratio, and pore structure of char on the pyrolysis tar removal were studied. The results showed that increasing pyrolysis temperature and char/biomass mass ratio would promote tar decomposition. When using GC15 as catalyst, tar yield was as low as 0.10 wt% at the temperature of 850°C and the mass ratio of 2. Gasification treatment increased the specific surface area of raw char from 284.1 to 342.7 m2/g (GC5) and 435.6 m2/g (GC15). Comparing the catalytic activity of lignite chars with commercial activated carbon demonstrated that mesopores were more influential than micropores in tar removal. In addition, water produced during biomass pyrolysis could in situ contribute to tar reforming and char gasification reactions. The results obtained in this study suggested that a cheaper coal char-based catalyst with excellent performance for biomass tar cracking could be achieved by combining with a coal gasification process and optimizing gasification conditions.

Syngas Production for Fischer-Tropsch Synthesis from Rubber Wood Pellets and Eucalyptus Wood Chips in a Pilot Horizontal Gasifier with CaO as a Tar Removal Catalyst.

This research aims to investigate steam biomass gasification in a pilot horizontal gasifier using rubber wood pellets (RWPs) and eucalyptus wood chips (EWCs) for producing syngas with an H2/CO ratio range of 1.8 to 2.3 for Fischer-Tropsch synthesis. The study was divided into two parts. One was carried out in a lab-scale reactor to determine the effect of temperature and CaO on the gas product composition and the efficiency of tar removal. Another part was determined by investigating the effect of the steam/biomass (S/B) ratio on the produced H2/CO ratios in the pilot horizontal gasifier, which used the optimum conditions of temperature and % loading of CaO for tar removal according to the optimal conditions from the lab-scale gasifier. The lab-scale gasifier results showed that H2 and CO2 increased with temperature due to primary and secondary water gas reactions and hydrocarbon reforming reactions. The water gas shift and hydrocarbon reforming reaction depressed the CO and CH4 contents with increasing temperature, respectively. The optimum gasifying temperature was 900 °C, which obtained H2/CO ratios of 1.8 for both RWPs and EWCs. The tar yield decreased with increasing temperature and was less than 0.2 wt % when using CaO as a tar-cracking catalyst. The operation of the pilot horizontal gasifier at the operating condition of 900 °C and a S/B ratio of 0.5 using 0.2 wt % loading of CaO for tar removal also produced a H2/CO ratio of 2.0. The supply of an external heat source stabilized the gasifying temperature, resulting in a stable syngas composition and production rate of 2.5 and 2.7 kg/h with H2/CO ratios of 1.8 and 1.9 for the RWPs and EWCs, respectively. In summary, the horizontal gasifier is another effective designed gasifier that showed high-performance operation.

Preparation of highly dispersed lignite-char-supported cobalt catalyst for stably steam reforming of biomass tar at low temperature

The removal of generated tar during the biomass gasification is a serious issue. Catalytic tar cracking is one of the most efficient methods to reduce tar deposition while many common tar cracking catalysts suffer problems of serious carbon deposition and active metal sintering, especially at low temperatures. Therefore, developing catalysts with both high activity and stability is critical. In this work, we aim to prepare catalysts with a high active metal contents, a small metal particle size and a high dispersion to contribute to the highly efficient tar removal at relatively low temperatures. By adjusting the type and the concentration of the Co precursor solution when lignite is used as the carbon precursor, we prepared a series of catalysts which were then applied for both activity and stability test of the steam reforming of model tar and biomass tar. The results show that Co0.15-C2H3O2− prepared with a 0.15 M solution of Co(C2H3O2)2·4H2O achieves a Co content of about 16.0 wt% with an average particle size of about 3.77 nm and a relatively high metallic Co dispersion. For steam reforming of toluene, the catalyst achieves an almost 100 % toluene conversion at 400 °C and exhibits a high stability in the 100 h test. Moreover, Co0.15-C2H3O2−, which produces approximately 283.8 mL.gcorncob−1.gcat−1.h−1 H2 catalytically, is also active and stable in biomass tar cracking. The catalyst prepared in the present study by using the economic and simple ion-exchange method also has a well-dispersed nano-metal-loaded structure and can efficiently remove the tar at a low temperature with a high stability, which will contribute to the industrial application in the future.

Catalytic activity evaluation and deactivation progress of red mud/carbonaceous catalyst for efficient biomass gasification tar cracking

Developing an efficient and inexpensive catalyst to remove tar is critical to biomass gasification technology. Herein, a red mud/carbonaceous catalyst was prepared by in-situ carbothermal reduction of sawdust and red mud and used in tar catalytic cracking with a two-stage fixed-bed reactor. Through the carbothermal reduction process, the catalyst was not only endowed with a porous carbon structure, but also reduced Fe2O3 in red mud to Fe0, which was beneficial to improve the catalytic activity and stability of the catalyst. The tar conversion efficiency of RM/SD catalyst reached 88.70% at the catalytic cracking temperature of 700 °C, which remained at 80.15% after nine cycles compared with RM (61.79%). The catalytic activity and deactivation progress of RM/SD catalyst were investigated by a variety of characterizations for the chemical states, crystallite sizes and pore structure of RM/SD catalyst after different cycles. Coke deposition and metal oxidation were the main reasons causing catalyst deactivation. During the tar catalytic cracking process, alkaline metals in red mud migrated to the surface of catalyst and cooperated with Fe active phase, which promoted the gasification of coke and alleviated the rapid deactivation of catalyst derived from coke deposition. Meanwhile, the presence of carbon support delayed the oxidation of metal active phase and made the catalyst keep a good tar catalytic cracking performance. Therefore, a potential scheme is proposed for the development and utilization of bauxite residue and forestry wastes for tar cracking.

Study of mayenite produced from waste eggshell as support for Ni–Co catalysts for biomass tar cracking

Ultrasonication-promoted synthesis was applied to produce mayenite (M-CES) with properties similar to mayenite produced with commercial reagents, using calcined eggshell waste as a calcium source. Monometallic 10Ni/M-CES (10 wt.% Ni) and 10Co/M-CES (10 wt.% Co) and bimetallic 5Ni5Co/M-CES (5 wt.% Ni and 5 wt.% Co) catalysts were synthesized by the wet impregnation method. Catalyst 10Co/M-CES showed a noticeably lower metal dispersion when compared to the Ni-containing catalysts. 5Ni5Co/M-CES bimetallic catalyst showed the highest metal dispersion, and XRD analysis proved the Ni–Co alloy formation. The performance of Ni–Co catalysts for hydrocarbon cracking was evaluated by methane and propane catalytic decomposition. The alloy formation between Ni and Co in the bimetallic catalyst provided a reduction in the start temperature of the cracking reaction of approximately 80 °C and 110 °C for methane and propane, respectively, when compared to monometallic catalysts. A synergistic effect was also observed by a decrease in carbon deposition and an increase in the catalytic activity of 5Ni5Co/M-CES. The use of eggshell waste to produce mayenite support for tar cracking catalysts has proved to be attractive to add value to the eggshell waste.

Utilization of Modified Zeolite as Catalyst for Steam Gasification of Palm Kernel Shell

Syngas from biomass gasification is being developed for alternative feedstock in the chemical industry. Palm kernel shell which is generated from palm oil industry can be potentially used as raw material for gasification process. The purpose of this study was to investigate the use of modified natural zeolite catalysts in steam gasification of palm kernel shells. Mordenite type zeolite was modified by acid leaching to be used as a tar cracking catalyst. Steam gasification was conducted at the temperature range of 750–850 °C and the steam to biomass ratio was in the range of 0–2.25. The result showed that steam gasification of palm kernel shell with the addition of zeolite catalyst at 750 °C and steam to biomass ratio 2.25 could reduce tar content up to 98% or became 0.7 g/Nm3. In this study, gasification of palm kernel shells produced syngas with the hydrogen concentration in the range of 52–64% and H2/CO ratio of 2.7–5.7. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synthesis of modified char-supported Ni–Fe catalyst with hierarchical structure for catalytic cracking of biomass tar

The ubiquitous challenge of tar problem has limited the further development of biomass pyrolysis/gasification. In view of this, the directional construction of modified char-supported Ni–Fe catalyst by hydrothermal carbonization followed by heat treatment to strengthen tar cracking was reported in this study. At the optimized temperature of 700 °C for catalytic cracking, the corresponding tar conversion efficiency of catalyst appeared to be 95.46% with the superior catalytic performance of tar. With the presence of such catalyst, the relative content of polycyclic aromatic hydrocarbon (PAH) compounds in residue tar was drastically reduced due to the high activity of Ni–Fe alloy active phases for the cleavage of tar macromolecules. The hierarchical pore structure derived from the dense carbon nanofiber shell layer and porous carbon core reduced the resistance of tar macromolecules diffusion and promoted the contact with metallic active sites. The Fe atoms enriched on the surface of Ni–Fe alloy with a high oxygen affinity promoted the catalytic cracking reaction of tar. The coated metallic active sites with multi-layer graphitic carbon prevented the catalyst from deactivation and sintering. The results are expected to establish the theory foundation and construction method of char-supported Ni–Fe catalyst for tar catalytic cracking in the industry.

Mechanism on catalytic cracking tar with CaO-based catalysts for hydrogen-rich gas by DFT and experiments

As the model compound of tar, the catalytic cracking performances of toluene with CaO-based catalysts were studied by DFT simulation and fixed bed experiment. The DFT results showed the adsorption energy of toluene on (1 0 0) surfaces increased as FC < CaO < NC < NFC at 650 °C. The optimal reaction path for toluene to dissociate H was obtained in the process of toluene cracking using NC and NFC catalysts. The NC catalyst doped with Fe enhanced the catalytic activity of Ni, and the rate determining step reaction activation barrier to generate H2 was decreased from 1.50 eV to 0.58 eV. And the activation barrier for CH4 formation was higher than that for H2, which promoted the cracking reaction to produce H2. The experimental results showed that the catalytic toluene cracking effect of NFC was the best among the four catalysts at 650 °C, with 98.11% conversion rate and 93.11% H2 yield. Compared with NC, H2 yield was increased by 27.92%, CH4 yield was decreased by 50.43%. Thermogravimetric results showed that NFC was less likely to be inactivated due to carbon deposition than NC. NFC will be a kind of compound catalyst for tar cracking with high efficiency.

Gasification of RDF and Its Components with Tire Pyrolysis Char as Tar-Cracking Catalyst

The composition of gas produced by the gasification of refuse-derived fuel (RDF) can be affected by the content of individual components of RDF and their mutual interactions. In this work, plastics, paper, wood, textile and RDF were gasified in a two-stage gasification system and the obtained tar yields and product gas quality were compared. The two-stage reactor consisted of an air-blown gasifier and a catalytic reactor filled with carbonized tire pyrolysis char as the tar-cracking catalyst. Tire pyrolysis char is a promising alternative to expensive catalysts. The impact of temperature and catalyst amount on the tar yield and gas composition was investigated. Theoretical oxygen demand for all material classes was calculated and its effect on gas composition and tar yield is discussed. The results indicate that the gasification of plastics produces the highest amount of tar and hydrocarbon gases, while the CO2 content of the product gas remains the lowest compared to all other materials. On the other hand, the paper fraction produced hydrogen-rich gas with low tar content. The gasification of RDF at 700 °C provided the lowest tar yield compared to all other materials, indicating positive synergic effects of lignocellulosic biomass and plastics in tar reduction. The significance of these interactions was suppressed at the highest temperature of 900 °C, as the thermal cracking of tar became dominant. For CO2 content, a negative synergic effect (higher CO2 concentration) was observed.

An Eco-Friendly Fluidizable FexOy/CaO-γ-Al2O3 Catalyst for Tar Cracking during Biomass Gasification

The present study deals with the development, characterization, and performance evaluation of an eco-friendly catalyst, using 2-methoxy-4-methylphenol (2M4MP) as a surrogate tar. The 2M4MP was selected due to its chemical functionalities and the fact that it is a good model compound to represent the tar formed during biomass low temperature gasification. The eco-friendly catalyst was prepared using the typical Fe and Ca minerals which are present in ash. These ash components were added to a fluidizable γ-Al2O3 support using a multistep incipient impregnation, yielding Fe oxides as an active phase and CaO as the promoter. The prepared catalyst displayed a 120 m2/g BET specific surface area, with few γ-Al2O3 bulk phase changes, as observed with XRD. TPD-NH3 and pyridine FTIR allowed us to show the significant influence of CaO reduced support acidity. A TPR analysis provided evidence of catalyst stability during consecutive reduction–oxidation cycles. Furthermore, catalyst evaluation vis-à-vis catalytic steam 2M4MP gasification was performed using the fluidized CREC riser simulator. The obtained results confirm the high performance of the developed catalyst, with 2M4MP conversion being close to 100% and with selectivities of up to 98.6% for C1-C2 carbon-containing species, at 500 °C, with a 7.5 s reaction time and 1.5 g steam/g 2M4MP. These high tar conversions are promising efficiency indicators for alumina catalysts doped with Fe and Ca. In addition, the used catalyst particles could be blended with biochar to provide an integrated solid supplement that could return valuable mineral supplements to the soil.

Catalytic tar conversion and the prospective use of iron-based catalyst in the future development of biomass gasification: a review

Biomass is a promising renewable energy source which is available globally, mostly in developing countries where access to clean and affordable energy is a critical problem. Biomass gasification is an interesting technology that can convert biomasses to a more versatile fuel known as syngas, the energy which can substitute conventional fossil fuels in the future. Syngas can amenably be combusted to produce power and heat as well as a feedstock for synthesis of chemicals and other fuels. The biomass gasification is facing severe operational challenges, one of the problems being tar formation and its removal techniques. Tar condenses at reduced temperature, thus causing blockage in the downstream equipment such as compressors and engines. Many studies have considered syngas cleaning by physical removal and thermal cracking unsuitable as they need downstream processing of scrub liquor and utilizes a part of the produced gas in maintaining the thermal cracking temperature, respectively. The utilization of catalysts has been an interesting focus; however, it has not yet been fruitful as many of the developed catalysts deactivate rapidly, and they are expensive or toxic. The motives of the current study are to review tar formation characteristics and trends on catalytic conversion. In addition, the study elucidates the fascinating behaviour of metallic and oxides of the iron-based catalyst under different syngas composition (oxidizing and reducing environments). The behaviours of the iron-based catalyst indicate its fundamental role in developing a catalyst for tar cracking with respect to less toxic, inexpensive, abundant, and regenerable alternatives.

Gas-Modified Pyrolysis Coke for in Situ Catalytic Cracking of Coal Tar.

Modified pyrolysis coke can be used as a catalyst for tar cracking. In this paper, pyrolysis coke was used as a carrier for modification by using gases (H2O, CO2, and NH3), and the optimal modified gas was selected. On the basis of this, pyrolysis coke with different modified flow rates, temperatures, and times were prepared to catalyze the cracking of tar. The effect of gas-modified pyrolysis coke on tar cracking products was studied. Also, pyrolysis coke was characterized by Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, and scanning electron microscopy. The results show that the optimal gas is H2O, and the optimal preparation conditions are 450 mL/min, 650 °C, and 60 min. The pyrolysis coke catalyst under the optimal conditions has the best cracking effect on tar. Also, the gas and tar yields have been further improved.

Highly active and stable HF acid modified HZSM-5 supported Ni catalysts for steam reforming of toluene and biomass pyrolysis tar

This paper investigated the performance of HF modified HZSM-5 supported nickel catalysts (Ni/FZ5) in steam reforming of toluene (TSR) and biomass pyrolysis tar (BSR). The mesopores volume of support increased from 0.021 to 0.061 cm3/g with decreasing acid amount from 2.27 to 0.41 mmol/g after HF treatment. Catalysts with different Ni loadings were prepared and characterized. The Ni/FZ5 with Ni loading of 9 wt% possesses relatively large specific surface area (337 m2/g) and average pore size (2.91 nm), as well as small Ni particle size (23 nm) and high dispersion. In the process of TSR, 9Ni/FZ5 was kept above 70% for 7 h. Owing to the calculated lower apparent activation energy (30.76 KJ/mol), 9Ni/FZ5 exhibited the best performance in BSR at 650 °C, achieving the largest H2 yield of 52.8 mmol/g and the highest selectivity of H2 at 72.8%. Additionally, only 1.6 mg/gcatalyst of coke deposition was detected. Moreover, its high activity was still identified with excellent hydrothermal stability even after 7 times of regeneration. All findings suggest that 9Ni/FZ5 is a promising catalyst for biomass tar cracking.

Pyrolysis Simulation of Thermally Thick Biomass Particles Based on a Multistep Kinetic Scheme

A new Eulerian-Lagrangian pyrolysis model is developed in the thermally thick regime to study the pyrolysis yields of large biomass particles based on a multistep kinetic scheme. The integrated pyrolysis model is first validated with experiments of centimeter-sized wood particles under both low- and high-temperature conditions. Good agreement is obtained between simulations and experimental measurements for low-temperature (375 and 470 °C) pyrolysis. However, for 800 °C pyrolysis, the predicted char, tar, and gas yields are not as accurately predicted as those of the low-temperature situation, while the overall gas and tar yields show an improvement when secondary tar decomposition is considered. Moreover, simulation results reveal that different sized particles generate similar char, tar, and gas yields, which account for about 30, 52, and 12% of the initial mass, respectively. Besides, a significant increase of the gas yield (∼70%) and a moderate decrease of the char yield (∼25%) are observed when the pyrolysis temperature increases from 400 to 700 °C, while the tar yield only changes slightly with first an increasing trend and then a decreasing trend with raising the pyrolysis temperature. The biomass type also has an important impact on both light gas and tar yields as a result of different components in each particle. Finally, effects of tar cracking and alkali metal catalyst on pyrolysis are also discussed.

Graphitic carbon embedded with Fe/Ni nano-catalysts derived from bacterial precursor for efficient toluene cracking

Highly-dispersed FeNi nano-catalysts embedded in bacterial derived graphitic carbon were successfully synthesized as sustainable and efficient tar cracking catalysts.

Modification of Natural Zeolite as a Catalystfor Steam Reforming of Toluene

A catalyst for tar cracking has been prepared successfully from natural zeolites using ion exchange with NH4NO3, and acid leaching with HNO3 solution for removing impurities and increasing pore volume. The activity of the modified zeolite was tested using toluene as a tar model compound. Tar conversion of about 54% was achieved in catalytic steam reforming at a temperature of 750C using 2 gram of catalyst and the gas hourly space velocity about 5040 h-1.

Modification of Natural Zeolite as a Catalystfor Steam Reforming of Toluene

A catalyst for tar cracking has been prepared successfully from natural zeolites using ion exchange with NH4NO3, and acid leaching with HNO3 solution for removing impurities and increasing pore volume. The activity of the modified zeolite was tested using toluene as a tar model compound. Tar conversion of about 54% was achieved in catalytic steam reforming at a temperature of 750C using 2 gram of catalyst and the gas hourly space velocity about 5040 h-1.

High quality H2-rich syngas production from pyrolysis-gasification of biomass and plastic wastes by Ni–Fe@Nanofibers/Porous carbon catalyst

To produce the high quality H2-rich syngas from biomass and plastic wastes, a two-stage pyrolysis-gasification system involving pyrolysis and catalytic gasification is considered as a suitable route. Generally, synthesis of highly active, low cost and coke-resistant catalyst for tar cracking is the key factor. A series of monometallic catalysts of Ni@CNF/PCs and Fe@CNF/PCs and the bimetallic Ni–Fe@CNF/PCs catalyst were prepared by a simple one-step pyrolysis approach for high quality syngas production from pyrolysis-gasification of biomass and plastic wastes. The results indicated that the bimetallic Ni–Fe@CNF/PCs catalyst appeared as the optimal catalyst in affording the best compromise between catalytic activity and stability with the existence of the excellent dispersibility of the Fe0.64Ni0.36 alloy nanoparticles and the carbon nanofibers/porous carbon composite structure. In addition, the optimal operation conditions of biomass/plastic ratio of 1/2 and gasification temperature of 700 °C were observed for the bimetallic Ni–Fe@CNF/PCs catalyst to play best roles in the H2-rich syngas quality, with up to 33.66 mmol H2/g biomass, and tar yields as low as 5.66 mg/g.

Potential of tire pyrolysis char as tar-cracking catalyst in solid waste and biomass gasification

Municipal solid waste (MSW) disposed in landfills is a serious environmental hazard and waste of potential source of reusable resources and energy as only a small portion of MSW is incinerated. Pyrolysis and gasification of MSW is an alternative to commercial combustion for the recovery of valuable chemicals and production of heat and electricity. Tar formation is a serious problem in the gasification process. Tar content in the product gas has to be decreased to a certain level required by the downstream production line. This can be achieved by the application of a suitable catalyst. However, commercial catalysts are expensive, prone to fast deactivation and sintering. Char from waste tire pyrolysis is a suitable catalyst for tar decomposition as it contains a significant amount of metals and has relatively large specific surface area. The advantage of this catalyst is its low price and no need for its regeneration as it can be simply combusted after losing its activity. In this work, catalysts prepared from tire pyrolysis char were activated at three different temperatures. The impact of activation temperature on the properties of prepared catalysts was analyzed. Tar cracking activity of the prepared catalysts was tested in a continuous tubular reactor and toluene was used as a model tar compound. Char activated at 900 °C achieved the highest toluene conversion and the lowest tar yield, so it was selected for application in batch gasification of refuse-derived fuel (RDF). During RDF gasification, the presence of a selected catalyst in the secondary reactor led to a decrease in the total amount of produced tar by 92.3% compared to non-catalytic (thermal) decomposition.

Catalytic gasification of refuse-derived fuel in a two-stage laboratory scale pyrolysis/gasification unit with catalyst based on clay minerals

Municipal solid waste (MSW) disposal is a serious environmental issue requiring immediate solution and good waste management strategy. Mechanical-biological treatment (MBT) plants offer the opportunity to reduce the amount of MSW that is, otherwise, disposed of in landfills. Up to 40% of MSW is converted to waste fuel, also called refuse-derived fuel (RDF). Gasification is a promising alternative of RDF processing. It can be defined as high temperature treatment of the feedstock with lower than stoichiometric amount of oxygen resulting mainly in a gaseous product (syngas). High hydrogen content, specific ratio of H2/CO, and low tar content are important parameters of syngas for its application in both energy production and chemical synthesis. Reduction of tar content in syngas can be achieved by catalytic tar cracking. In this work, a catalyst prepared from natural clay was characterised by thermogravimetric, specific surface area, X-ray diffraction, X-ray fluorescence and scanning electron microscopy (SEM) analyses. Catalyst activity was tested in two reactions, namely in decomposition of model tar constituent, p-xylene, and in cracking of tar produced in RDF gasification experiments. Influence of the reaction temperature and the amount of catalyst on the p-xylene conversion and products’ distribution was studied. The results proved high catalytic activity of the prepared catalyst in the decomposition of p-xylene. Coupled RDF pyrolysis and the produced volatiles gasification experiments were carried out in a two-stage laboratory scale reactor using a bed of tar cracking catalyst in the second stage. Tar decomposition experiments were carried out at the reactor temperatures of 700–850 °C applying different amounts of catalyst (0.75 g, 1 g, 1.25 g, 1.5 g, 2 g and 4 g) per 1 g of pyrolised RDF. Results indicate that the presence of catalyst had significant effect on both tar cracking efficiency and gas composition. Loss of the catalyst specific surface area was observed when the experiments were carried out at temperatures exceeding 800 °C.